Senate GOP leaders called on the Justice Department to divulge the level of involvement Supreme Court Justice Elena Kagan had in consulting on health care legislation that will be considered before the high court next year.

Kagan served as President Barack Obama's solicitor general prior to her appointment to the Supreme Court and conservatives have openly questioned her ability to consider the health care law as a sitting judge.

In a letter to Attorney General Eric Holder, leaders including Minority Leader Mitch McConnell (Ky.) and Minority Whip Jon Kyl (Ariz.) wrote that "when a former member of the administration is in a position to rule on litigation in which she apparently had some involvement and which concerns legislation she herself supports, public confidence in the administration of justice is undermined."

"Your department's refusal to provide information to the Congress that could eliminate this apparent conflict of interest only undermines that confidence further," they wrote in the letter, which was also signed by Judiciary ranking member Sen. Chuck Grassley (Iowa) and Sen. Mike Lee (Utah).

The Senate letter was sent the same day that 52 Democratic House Members called on the Judicial Conference, the governing body of the federal court system, to recommend that the DOJ look into whether Justice Clarence Thomas properly disclosed his wife's income. Virginia Thomas has worked at the Heritage Foundation, a conservative organization that has publicly criticized Obama's sweeping health care law. She also has been involved in the tea party movement.